[PATCH 2/2] x86/hvm: fix write emulation of RO ranges

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

When running on AMD hardware in HVM mode the guest linear address (GLA)
will not be provided to hvm_emulate_one_mmio(), and instead is
unconditionally set of ~0.  As a consequence mmio_ro_emulated_write() will
always report an error, as the fault GLA generated by the emulation of the
access won't be ~0.

Fix this by only checking for the fault GLA in mmio_ro_emulated_write()
when the guest is PV.

Fixes: 33c19df9a5a0 ('x86/PCI: intercept accesses to RO MMIO from dom0s in HVM 
containers')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/mm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 4fecd37aeca0..79836705c51e 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5187,7 +5187,12 @@ int cf_check mmio_ro_emulated_write(
 
     /* Only allow naturally-aligned stores at the original %cr2 address. */
     if ( ((bytes | offset) & (bytes - 1)) || !bytes ||
-         offset != mmio_ro_ctxt->cr2 )
+         /*
+          * HVM domains might not have a valid fault GLA in the context, as AMD
+          * NPT faults don't report the faulting GLA.  It's also possible for
+          * the fault to happen in non-paging modes.
+          */
+         (is_pv_domain(current->domain) && offset != mmio_ro_ctxt->cr2) )
     {
         gdprintk(XENLOG_WARNING, "bad access (cr2=%lx, addr=%lx, bytes=%u)\n",
                 mmio_ro_ctxt->cr2, offset, bytes);
-- 
2.48.1